In a sealing structure that has a torsional vibration damper and an oil seal, a technique of providing a labyrinth structure has hitherto been known for minimizing entrance of foreign substances from outside. One example of such a structure will be described with reference to FIG. 3. FIG. 3 is a schematic cross-sectional view of a sealing structure according to a prior art example.
As shown in the figure, the torsional vibration damper 600 includes a tubular part 610 that is attached to a crankshaft 300. The oil seal 500 includes an oil lip 510 provided such as to be slidable on an outer circumferential surface of the tubular part 610, and a dust lip 520 provided further on the opposite side from the sealed-fluid side than the oil lip 510 and slidable on the outer circumferential surface of the tubular part 610.
In this prior art example, a side lip 530 is provided to the oil seal 500. An annular groove 621 is formed in a body part 620 of the torsional vibration damper 600, and the side lip 530 is disposed such as to extend into this annular groove 621. This way, a confined and complex path is formed from the air side to a sliding part between the dust lip 520 and the outer circumferential surface of the tubular part 610. A labyrinth structure is thus provided.
However, in some cases where the difference between the inner diameter and the outer diameter of the oil seal 500 needs to be small, the side lip 530 cannot be provided in the prior art example described above. In such cases, the labyrinth structure that makes use of the side lip 530 cannot be adopted.